In recent years, organic EL displays using electroluminescence (EL) of an organic material have been attracting attention as a type of next-generation flat panel display replacing liquid crystal displays.
Unlike the voltage-driven liquid crystal display, the organic EL display is a current-driven display device. Accordingly, there is an urgent need for development of a thin-film transistor having excellent characteristics as a driving circuit for the active-matrix display device. The TFT is used as a switching device for selecting a pixel or a driving transistor for driving the pixel.
With reference to FIG. 11, a configuration of a conventional pixel circuit shall be described. A pixel circuit 900 illustrated in FIG. 11 includes a substrate 910, and a semiconductor device part and a capacitor part that are formed above the substrate 910. The semiconductor device part is a bottom-gate thin-film transistor formed by stacking a gate electrode 921, a gate insulating film 930, a crystalline silicon layer 941, a non-crystalline silicon layer 951, a channel protective layer 960, a pair of contact layers 971 and 972, a source electrode 981 and a drain electrode 982 above the substrate 910. The capacitor part is formed by stacking a first capacitor electrode 922, a gate insulating film 930 that serves as a dielectric layer, a first silicon layer 942, a second silicon layer 952, a third silicon layer 973, and a second capacitor electrode 983 above the substrate 910.
The semiconductor device part is a channel-protective (etching-stopper) thin-film transistor having the channel protective layer 960 for protecting, from etching, the crystalline silicon layer 941 that serves as a channel layer. The channel-protective thin-film transistor can prevent the damage on the channel layer due to etching, and can suppress the variation in the characteristics in the substrate 910, as disclosed in the patent literatures 1 and 2, for example. Furthermore, with the channel-protective thin-film transistor, it is possible to reduce the thickness of the channel layer. This allows reducing parasitic resistance component, thereby improving the on-characteristics. For that reason, the channel-protective thin-film transistor is useful for improving definition.